Definition
Yaws is a chronic infection caused by the bacteria Treponema pallidum, subspecies pertenue , which primarily affects the skin, bones, and joints.

Alternative Names
Frambesia tropica

Causes, incidence, and risk factors

Yaws is an infection caused by the spiral-shaped bacterium (spirochete) called Treponema pertenue. It is closely related to the organism that causes syphilis, but this disease is not sexually transmitted. Yaws mainly affects children in rural, warm, tropical areas -- primarily Caribbean Islands, Latin America, West Africa, India, and Southeast Asia.

Yaws is transmitted by direct contact with skin lesions of infected people. Approximately two to four weeks after infection, the child develops a sore mother yaw where the organism entered the skin.

The sore appears as a raspberry-like growth or group of papules at the site of infection and is usually painless. These lesions may persist for months. Additional satellite lesions may appear shortly before or after the mother yaw heals. Children may also develop inflammation of the bones and fingers.

The final stage involves destructive lesions of the skin and bones which can lead to severe disfigurement and disability. It occurs in up to 20% of untreated individuals.

Prevention
Mass campaigns for eradication of yaws via penicillin treatment in the 1950s and 1960s have dramatically decreased the worldwide incidence of yaws.

Symptoms

Initial, single skin lesion that may grow slowly and have a raspberry-like appearance. It may also form an ulcer and is usually painless.
Satellite lesions which may become large nodules/growths throughout the body and may have superficial erosions in secondary yaws.
Fever may be present in secondary yaws.
Bone pain/bone destruction; saber shins.
Finger inflammation (dactylitis).

Signs and tests
The diagnosis can be confirmed by examining a sample from a skin lesion under special type of microscope (darkfield examination). There is no specific blood test for yaws, but because it is closely related to the bacterium that causes syphilis, the blood tests for syphilis may be positive in yaws as well.